In some communication systems, wireless communication devices operating in these systems are required to monitor receive frequencies for multiple scan members on a scan list for radio frequency (RF) activity. To perform the monitoring, the wireless communication device switches between the receive frequency for each scan member on the list and scans or monitors for a signal of interest. If no signal of interest is found that corresponds to a given scan member, the wireless communication device tunes to the receive frequency of the next scan member to monitor for a signal of interest, and so on through the scan list.
A wireless communication device currently encounters some problems while traversing its scan list. Namely, as the number of scan members on the scan list increases, the amount of time between consecutive visits to a particular scan member on the scan list also increases. Moreover, as the time between consecutive visits to a particular scan member increases, the chances to arrive late to or completely miss a signal of interest increases. The net result of arriving late to a voice transmission is that the user may miss the first few words of a voice transmission. In other words, the user experiences voice truncation. The operational impact to late entry and, therefore, truncation is often described by the “Don't Fire!” example, wherein “Don't Fire” was transmitted, but the user hears “Fire” due to the voice truncation. Thus, even a single second of truncation can drastically change the meaning of a communication.
A known method of monitoring multiple frequencies at the same time is for the wireless communication device to be configured with a receiver circuit for each frequency being monitored. This would indeed address the problem, but this approach quickly becomes impractical and expensive as the number scan members and frequencies that need to be monitored increases.
Other approaches involve attempting to enhance the scanner hardware in the wireless communication device to more quickly switch between the receive frequencies associated with the scan members and more quickly detect RF energy on any given receive frequency. However, this approach can only take a scanner's optimization so far. The biggest impact to a scanner's ability to traverse the wireless communication device's scan list is interference, which, as the term is used herein, is defined as any signal on a receive frequency that is not of interest. More particularly, although it may only take tens of milliseconds to identify a receive frequency as free of RF energy; in some cases (for example when scanning for digital signals) it may take into the range of 500 ms to identify a signal present on a receive frequency as being of interest or not of interest. This is because, a scanner of digital signals must not only detect RF energy, it must synchronize to the receive frequency and read embedded identifiers before determining whether or not a detected signal is of interest. To minimize these times usually requires changes to over-the-air protocols used in the system, and such protocol changes may not always be possible.
Thus, there exists a need for a method and device for traversing a scan list for a wireless communication device.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments. In addition, the description and drawings do not necessarily require the order illustrated. Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.